Numerical Investigation Of Bowed Blades And Leaned Guide Vanes On Performance And Aerodynamic Noise Of Axial Flow Fans

With the acceleration of"carbon peak"and"carbon neutral",the installed capacity of wind turbines and photovoltaics is growing rapidly,and the task of peak-shaving of power generation units is increasingly urgent.A two-stage variable-pitch axial fan has been widely applied due to its high regulation efficiency and good air conducts adaptability.Taking a two-stage variable-pitch axial fan of a 600 MW power generation unit as an example,Fluent is employed to perform a three-dimension simulation of the fan.On the premise of ensuring an accurate model,the performance and aerodynamic noise of bowed blades and leaned vanes on axial flow fans are explored,the internal dynamics and the noise characteristics are examined,as well as all different cases are compared.Results show that the positively bowed blades can improve the performance of the fan.At the design condition,the total pressure rise is the highest when the positively bowed angle is 40°with the increase of 232 Pa,while the efficiency is the largest when the positively bowed angle is 20°with an increase of 0.16 percentage point.After blades are positively bowed,the low-energy fluids near the blade tip and root migrate to the middle part of blades,reducing the flow losses in the tip and root regions.Moreover,the positively bowed blades have a greater influence on the second stage impeller than the first stage impeller.The positively bowed blades reduce the overall sound pressure level in the rotor regions.The overall sound pressure level at the first stage rotor of B40 case decreases by 5.87 d B,and the overall sound pressure level at the second stage rotor decreases by 2.46 d B.The fan performance reduces after leaning guide vanes,and at the same lean angle,the reduction extent of the performance parameters of the negatively leaned guide vanes is greater than that of the positive leaning.After leaning guide vanes,the axial velocity at the middle of the flow channel weakens and the entropy production rate increases.When employing positively leaned guide vanes,the overall sound pressure level in both two stage guide vanes decreases,and the higher the lean angle,the more significant the reduction of the overall sound pressure level.The noise reduction effect of the second stage guide vanes is better than that of the first stage,and its noise reduction is mainly the reduction of tonal noise.When utilizing negatively leaned guide vanes,the noise of the first stage guide vanes is basically unchanged,while the overall sound pressure level of the second stage guide vanes raises by 2.5 d B.The total pressure rise of the fan with bowed blades and leaned vanes are improved,and the total pressure rise of the fan with B40SP15 is increased by about172 Pa at design point.The combined bowed blades and lean vanes make the efficiency reach the maximum at Q=85 m³·s^-1,which is 0.39 percentage point higher than the original fan.The overall sound pressure level at all monitoring points is significantly reduced,and the noise reduction is the most significant in the second stage blade area.A comparison of different cases shows that the efficiency curve of the positively bowed blade is gentle,whereas that of the combination of bowed blades and leaned vanes is steeper.Therefore,the bowed blades are more suitable for the peak-regulating power units.The noise reduction of the combination of bowed blades and leaned vanes is better than that of the bowed blades and leaned vanes at Q=85m³·s^-1,and the bowed blades can reduce the broadband noise increased by leaned vanes.